Chamber-type doctor blade devices which are designed to supply printing fluids such as inks and varnishes to the applicator roller of a printing machine are known in the art. For example, DE-A-1,761,439, DE-B-1,806,140 and EP 0,071,180 A1 all teach chamber-type doctor blade devices. These chamber-type doctor blade devices are typically mounted upon a carrier which enables them to be positioned in engagement with the applicator roller of a printing press. Generally, a chamber-type doctor blade apparatus includes a housing having side walls which are formed by sliding seals such as the apparatus described in the publication WO 89/07047. The housing of the chamber-type doctor blade apparatus combines with a working doctor blade which is assigned to the applicator roller over a predetermined length to form a chamber for receiving the printing fluids from a supply line. The housing and the working doctor blade form an open channel or face adjacent the applicator roller which permits the fluids received through the supply line to flow to the applicator roller.
As taught by DE-B-1,806,140, the end of the chamber opposite the working doctor blade can be open, or, as illustrated in DE-A-1,761,439 and EP 0,071,180 A1, the chamber can be provided with a closing doctor blade which seals the open end of the chamber and combines with the working doctor blade and housing to form a closed chamber. When a closed chamber construction is employed, the working doctor blade and the closing doctor blade are brought into engagement with the applicator roller and, together with the side walls, provide a sealed enclosure which ensures the printing fluids can only exit the chamber through the open channel adjacent the applicator roller. Regardless of the type of chamber employed (i.e. open-ended or closed), the doctor blades (also simply called blades) are generally fastened to the housing by screw connections.
As mentioned above, chamber-type doctor blade devices of many different constructions are known in the art. For example, DE 3,838,546 C2 illustrates a chamber-type doctor blade apparatus having laterally non-displaceable doctor blades which can be placed loosely in a slot; DE 3,832,216 C1 illustrates doctor blades which are non-detachably arranged in a housing body; DE 3,909,879 C1 illustrates an integral chamber-type doctor blade apparatus (housing and doctor blade elements) arranged detachably on a carrier by means of a plug-in connection; and, DE 3,823,340 C1 illustrated a chamber-type doctor blade apparatus which receives at least one additional doctor blade inside the chamber. The additional blade taught by DE 3,823,340 C1 is intended to provide better wettability of the cells on the applicator roller to prevent so-called "ghosting".
Prior art chamber-type doctor blade devices suffer from many disadvantages. For instance, it is very expensive to replace a worn doctor blade in these printing machines because, in order to remove a doctor blade, the printing machine must be stopped. For example, in order to replace a worn working doctor blade, printing has to be interrupted and the chamber-type doctor blade apparatus has to be pivoted away or uncoupled from the applicator roller. Usually, the housing of the chamber-type doctor blade must be emptied to perform this procedure.